1. Field of the Invention
The present invention relates to an insert injection molding method in which an insert is located in a mold in advance of a molten molding material injection and then molded by molding material at its outer peripheral sides of the insert to obtain a molded part integrally formed with the insert and the molding material, and also relates to its jig used in the injection method.
2. Description of the Related Art
An insert injection molding method of this kind is disclosed in Japanese patent laying-open publication (Tokkaihei) No. 11-277579. In this method, an insert, such as a pipe, is positioned in a mold in advance of a molten molding material injection, reinforced with a core pin arranged in a hole of the insert against pressure of the molding material during injection. The core pin is made smaller in diameter than the hole of the insert to have a gap between them for easy inserting and drawing-out.
The above known conventional method, however, encounters such a problem in that the gap between the insert and the core pin can not prevent from causing deformation of the insert, especially when the insert has a flat or plane portion, for the plane portion can be easily deformed by molten molding material injected under pressure as compared with a round portion. When the gap is set smaller in order to minimize the above disadvantage, the core is inserted into or drawn out of the insert in a press fit state to generate a large friction force between them during its inserting and drawing-out, thereby causing troublesome work.
It is, therefore, an object of the present invention to provide an insert injection molding method which overcomes the foregoing drawbacks and in which a core can be easily inserted into and drawn out of an insert having a plane surface, and a molded part can be formed without deformation of the insert caused by a molten molding material injected under pressure.
It is another object of the present invention to provide a jig which can be used suitably for the above insert injection molding method.